URI student uncovers threat to butterfly population
Invasive plant kills monarch larvae
KINGSTON, R.I. -- September 12, 2000 -- North Kingstown resident
Jennifer Dacey, a senior at the University of Rhode Island, spent the summer
investigating an invasive plant that could reduce local populations of monarch
Working with URI Professor Richard Casagrande, Dacey studied black swallowwort,
a plant native to Europe that kills the larvae of America's most popular
"The objective of my study was to see how this invasive plant affects
monarch populations," said Dacey. "Our laboratory made what we
believe is the first scientific observation of monarch's laying eggs on
That behavior could be bad news for the butterfly.
Monarch caterpillars feed exclusively on milkweed, a common native plant
that serves as a host to several insect species. Each adult female monarch
lays 200 to 300 eggs in the summer.
"If they lay their eggs on black swallowwort, the eggs hatch but
the larvae don't survive," Dacey explained. "That's most likely
because the plant has a different toxicology than milkweed, so after feeding
on it once, they die."
Black swallowwort was brought to New England in the 1800s to cultivate
as an ornamental plant, but it quickly spread throughout the Northeast.
It grows in disturbed areas like roadsides, and has begun to expand into
backyards and natural areas. The plant is difficult to control with herbicides,
and even pulling it out by hand doesn't eliminate it.
"There aren't any native insects that keep it under control here,
and it usually outcompetes native vegetation," Dacey said.
Dacey studied captive monarchs in cages in a lab and in the field, and
she checked more than 1,000 black swallowwort plants in fields in North
Kingstown, Wakefield, Kingston and Jamestown during
July and August. She observed that monarchs prefer to lay eggs on milkweed,
but a substantial portion of their eggs are laid on swallowwort. If this
invasive weed continues to spread, it might seriously reduce monarch populations.
Dacey's research was funded by the URI Coastal Fellowship Program, a
unique program designed to involve undergraduate students in addressing
current environmental problems. Sponsored by the URI Cooperative Extension
and now in its fifth year, the Coastal Fellowship Program teams students
with URI faculty, research staff and graduate students to help undergraduates
gain skills that will ensure their future success.
Following graduation in May 2001, Dacey hopes to conduct additional
fieldwork involving mammals, birds or insects.
"My black swallowwort research has given me a greater appreciation
for plants," she said. "I believe my Coastal Fellowship played
an important role in setting a foundation for my future endeavors and gave
me a competitive edge in the process."
For Information: Todd McLeish 874-7892